Field of the Invention
The present invention relates to a machine tool having a function of detecting the attachment state of protective covers.
Description of the Related Art
In general, many of machine tools with CNC are configured so that a machining area is covered by protective covers to prevent chips or a cutting fluid from scattering or splashing during machining. The protective covers include “fixed protective covers” without a movable mechanism and “movable protective covers” with the movable mechanism.
A movable protective cover is provided for an operation to place a workpiece to be machined in the machining area. Further, the fixed protective covers can be classified into “non-removable fixed protective covers” and “removable fixed protective covers”. The non-removable fixed protective covers are not supposed to be removed in the general use of machine tools, due to problems including their weight, mounting method, and necessity. The removable fixed protective covers can be easily removed although they are not supposed to be removed in normal use.
The movable protective cover is designed to be opened or closed after the start or completion of machining, in order to secure the workpiece in the machining area, for example. As disclosed in Japanese Patent Application Laid-Open No. 2009-187531, therefore, the open/close state of the movable protective cover is monitored for safety by a numerical controller (CNC) using a safety lock mechanism. For example, a limit is set such that an automatic operation mode cannot be started unless the movable protective cover is closed, for example. Since the safety lock mechanism is expected to forcibly maintain the closed state in view of safety, it is generally a mechanical lock mechanism.
However, the safety lock mechanism of this type is intended to monitor the open/close state of the movable protective cover only, and unlike that of the present invention described later, cannot monitor the attachment state of the fixed protective covers together. This is because the fixed protective covers are inherently fixed metal plates that surround the machine tool and are not supposed to be objects of monitoring.
Further, operations to open and close the covers are omitted in actual use. If the safety lock mechanism is modified so that the CNC may be forced to misunderstand that the covers are closed, the machine tool may sometimes be automatically operated with the covers open, resulting in a safety problem.
In some cases, the removable fixed protective covers may be temporarily removed during maintenance work for the machine tool, such as cleaning in the machining area. Unlike the movable protective cover to be opened and closed, however, the fixed protective covers generally are not designed to be mounted and removed, so that their attachment state is not monitored by the CNC in many cases. Therefore, the machine tool is allowed to be automatically operated even when the fixed protective covers are carelessly left unattached after the maintenance work or the like. In such a case, the same safety problem for the case of the movable protective cover with the modified safety lock mechanism may be caused.
If these protective covers are in abnormal positions, e.g., inclined positions, although they do not fail to be attached, moreover, a cutting fluid or chips of the workpiece may possibly splash or scatter out of the protective covers during machining or the fixed protective covers may cause an accident by dropping or the like.
As described in Japanese Patent Application Laid-Open No. 2008-158914, for example, there is a known technique for detecting the attachment state of a protective cover of a machine. In this technique, a contactor and a terminal are attached to the main body of an electronic apparatus and the cover, respectively, so that they contact each other when the cover is closed, whereby the attachment of the cover can be electrically detected.